creates error_handler middleware to replace decorator on all pages
fixes broken import
has middleware only display user defined exceptions and allows raising of custom status code
adds comments and tests to error middleware
deletes old decorator
changes post param missing to renderable error and test for it
adds canvas tests for 100% coverage
cancel buttons added
Changes GET to POST for selection pages
Merge branch 'feature/track_activation' into feature/cancel_changes
adds errors in middleware to subclass django errors so that correct status codes are still raised even if middleware isn't installed
changes errors defined in ab_testing_tool to use new dual-errors
streamlines some execption behavior
allows overriding default error message and template name in settings
eliminates dependence of error middleware on ab_testing_tool so that it can become its own project
Merge pull request #24 from penzance/feature/cancel_changes

Feature/cancel changes
Merge pull request #20 from penzance/feature/error_middleware

Changes error handling from a view decorator to middleware